1. Field of the Invention
The present invention relates to a semiconductor device and a method for manufacturing the semiconductor device, particularly, a method for manufacturing a semiconductor device using a thin film transistor.
2. Description of the Related Art
In recent years, IT (Information Technology) penetrates the world due to the propagation of the Internet, which has brought revolution. In particular, as expressed as a ubiquitous information society, nowadays, the environment making it possible to access networks everywhere at any time has been developed. In such an environment, individual verification technologies attract attention, in which an ID (identification code) is assigned to an individual object thereby specifying the history of the object and it is applied to production, management, or the like.
Among them, currently, a semiconductor device in which a micro IC chip manufactured using a single crystal Si substrate and an antenna for wireless communication are combined (also referred to as an RFID (Radio Frequency Identification) tag, an ID tag, an IC tag, a wireless tag, a wireless chip, or an electron tag) are spotlighted. The semiconductor device makes it possible to write data or read data by using a wireless communication device (hereinafter referred to as a “reader/writer”).
As an application field of such a semiconductor device, for example, product management in distribution industry can be given. At present, product management using barcodes or the like is a mainstream; however, since data of barcodes are read optically, they cannot be read when a shield exists. On the other hand, as to the semiconductor device described above, since data are read wirelessly, they can be read even when a shield exists. Thus, higher efficiency, lower cost, and the like of product management are expected. In addition, wide use of the semiconductor devices in IC cards, labels provided with IC tags, tickets, air tickets, automatic checkout, and the like is expected (for example, Reference 1: Japanese Published Patent Application No. 2002-366917 and Japanese Published Patent Application No. 2002-123805).
Further, for providing semiconductor devices such as RFID tags or the like on a variety of products, it is desirable to provide the semiconductor devices at low cost. However, in the case of manufacturing a semiconductor device using a single crystal Si substrate, since a single crystal Si substrate is expensive, reduction in cost is limited. In addition, Si substrates are used in different fields so that there are concerns of the short supply of Si substrates if a great number of Si substrates are used. Therefore, when a single crystal Si substrate is used, cost reduction is more difficult.
Meanwhile, in order to provide semiconductor devices at low cost, techniques in which a semiconductor device is formed using a semiconductor thin film formed over a glass substrate or a plastic substrate are studied. In the case of using such a substrate, the area and the shape are not particularly limited. For example, when a rectangular shape having 1 meter or more on one side is used, improvement in productivity and reduction in manufacturing cost are expected as compared with the case of using a circular silicon substrate.
Further, when a semiconductor device using a semiconductor film is manufactured, a crystalline semiconductor thin film is used to improve the signal processing speed and the like of the semiconductor device. However, there are problems in that the processing speed, communication distance, and the like depend on a crystal state of the semiconductor thin film formed over a substrate, or the layout of circuits formed using the semiconductor thin film or the like, for example. Hereafter, cost reduction, high processing speed, and longer communication distance with respect to such semiconductor devices are increasingly required.